Prolactin receptors are being purified from rat liver and rabbit mammary glands by solubilization by detergents and subsequent affinity and hydrophobic chromatography. Fluorescence polarization was examined as a possible means of assaying for prolactin receptor. Fluorescein-Prolactin was prepared and it interacted with receptor. However, unlabelled prolactin did not displace the fluorescein-prolactin from the receptor. Subsequent studies showed that fluorescein-prolactin interacted with bovine serum albumin which was present in the buffer. The use of Triton X-100 as a detergent resulted in high non-specific binding due to interaction with the detergent. Zwitterionic detergents appear to be very useful for purification of the prolactin receptor and they reduce the non-specific binding.